1. Field of the Invention
This invention relates generally to methods and compositions useful for controlling sand production from subterranean formations. In particular, this invention relates to use of relatively lightweight and/or substantially neutrally buoyant particles as particulate material in sand control methods such as gravel packing, frac packs, etc.
2. Description of the Related Art
Production of particulate solids with subterranean formation fluids is a common problem. The source of these particulate solids may be unconsolidated material from the formation, proppant from a fracturing treatment and/or fines generated from crushed fracture proppant. Production of solid proppant material is commonly known as xe2x80x9cproppant flowback.xe2x80x9d In addition to causing increased wear on downhole and surface production equipment, the presence of particulate materials in production fluids may also lead to significant expense and production downtime associated with removing these materials from wellbores and/or production equipment. Accumulation of these materials in a wellbore may also restrict or even prevent fluid production. In addition, loss of proppant due to proppant flowback may also reduce conductivity of a fracture pack.
In an effort to control or prevent production of formation or proppant materials, many methods have been developed. Included among these are those methods commonly referred to as gravel packing and frac packs. These methods commonly employ particulate materials that are placed downhole with a gelled carrier fluid (e.g., aqueous-based fluid such as gelled brine). Gelling agents for gelling carrier fluids may provide a source of formation damage. Formulation of gelled carrier fluids usually requires equipment and mixing steps designed for this purpose.
In the disclosed method, the application of relatively lightweight and/or substantially neutrally buoyant particulate material as a sand control particulate advantageously may provide for substantially improved overall system performance in particulate-based sand control methods such as gravel packing and frac packing. By xe2x80x9crelatively lightweightxe2x80x9d it is meant that a particulate has a density that is substantially less than a conventional particulate material employed in particulate-based sand control methods, e.g., conventional gravel packing gravel, sand or having a density similar to these materials. By xe2x80x9csubstantially neutrally buoyantxe2x80x9d, it is meant that a particulate has a density sufficiently close to the density of a selected ungelled or weakly gelled carrier fluid (e.g., ungelled or weakly gelled completion brine, other aqueous-based fluid, or other suitable fluid) to allow pumping and satisfactory placement of the particulate using the selected ungelled or weakly gelled carrier fluid. For example, urethane resin-coated ground walnut hulls having a specific gravity of from about 1.25 to about 1.35 grams/cubic centimeter may be employed as a substantially neutrally buoyant sand control particulate in completion brine having a density of about 1.2. It will be understood that these values are exemplary only. As used herein, a xe2x80x9cweakly gelledxe2x80x9d carrier fluid is a carrier fluid having minimum sufficient polymer, viscosifier or friction reducer to achieve friction reduction when pumped down hole (e.g., when pumped down tubing, work string, casing, coiled tubing, drill pipe, etc.), and/or may be characterized as having a polymer or viscosifier concentration of from greater than about 0 pounds of polymer per thousand gallons of base fluid to about 10 pounds of polymer per thousand gallons of base fluid, and/or as having a viscosity of from about 1 to about 10 centipoises. An ungelled carrier fluid may be characterized as containing about 0 pounds per thousand gallons of polymer per thousand gallons of base fluid.
Advantageously, in one embodiment use of substantially neutral buoyancy particulate material may eliminate the need for gellation of carrier fluid, thus eliminating a source of potential formation damage. Furthermore, use of a relatively lightweight particulate material typically means that a much reduced mass of relatively lightweight particulate material is required to fill an equivalent volume than is required with conventional sand control particulates used, for example, for gravel packing purposes. Elimination of the need to formulate a complex suspension gel may mean a reduction in tubing friction pressures, particularly in coiled tubing and in the amount of on-location mixing equipment and/or mixing time requirements, as well as reduced costs. Furthermore, when treated to have sufficient strength (e.g., by substantially filling the permeable porosity of a porous particle with resin or hardener), the disclosed relatively lightweight sand control particles may be employed to simplify sand control treatments performed through coil tubing, by greatly reducing fluid suspension property requirements. Downhole, with a much reduced propensity to settle (as compared to conventional sand control particulates), more efficient packing particularly in highly deviated or horizontal wellbore sections) may be achieved. In this regard, the disclosed substantially neutral buoyancy particulate material may be advantageously employed in any deviated well having an angle of deviation of between about 0 degree and about 90 degrees with respect to the vertical. However, in one embodiment, the disclosed particulate material may be advantageously employed in horizontal wells, or in deviated wells having an angle with respect to the vertical of between about 30 degrees and about 90 degrees, alternatively between about 75 degrees and about 90 degrees.
Elimination of the need to formulate a suspension gel advantageously may mean a reduction in tubing friction pressures (particularly in coiled tubing), a reduction in the amount of on-location mixing equipment and/or mixing time requirements, as well as reduced costs. Thus, use of the disclosed relatively lightweight and/or substantially neutrally buoyant particulate materials disclosed herein may be employed to achieve surprising and unexpected improvements in sand control methodology and results, including reduction in formation damage and enhancement of well productivity.
In another embodiment, protective and/or hardening coatings, such as resins described elsewhere herein may be selected to modify or customize the specific gravity of a selected base particulate material, e.g., ground walnut hulls, etc. Modification of particulate specific gravity (i.e., to have a greater or lesser specific gravity) may be advantageously employed, for example, to provide sand control particulates of customized specific gravity for use as a substantially neutrally buoyant particulate with a variety of different weight or specific gravity carrier fluids. In yet another embodiment, protective and/or hardening-type coatings may be optionally curable to facilitate sand control particulate consolidation after placement. In this regard, curable resins are know to those of skill in the art, and with benefit of this disclosure may be selected to fit particular applications accordingly.
The disclosed relatively lightweight and/or substantially neutrally buoyant particulate materials may be employed with carrier fluids that are gelled, non-gelled, or that have a reduced or lighter gelling requirement as compared to carrier fluids employed with conventional sand control methods, e.g., conventional gravel packing methods. In one embodiment employing one or more of the disclosed substantially neutrally buoyant particulate materials and a brine carrier fluid, mixing equipment need only include such equipment that is capable of (a) mixing the brine (dissolving soluble salts), and (b) homogeneously dispersing in the substantially neutrally buoyant particulate material.
In one embodiment, a substantially neutrally buoyant particulate material may be advantageously pre-suspended and stored in a storage fluid (e.g., brine of near or substantially equal density), and then pumped or placed downhole as is, or diluted on the fly.
In one respect, disclosed is a sand control method for a well penetrating a subterranean formation, including introducing a relatively lightweight and/or substantially neutral density particulate material into the well. Individual particles of the particulate material optionally may have a shape with a maximum length-based aspect ratio of equal to or less than about 5. Individual particles may also be optionally coated with protective materials such as resins and/or hardeners, for example, xe2x80x9c2ACxe2x80x9d phenol formaldehyde hardener from BORDEN CHEMICAL. Examples of suitable relatively lightweight and/or substantially neutrally buoyant materials for use in aqueous based carrier fluids include, but are not limited to, ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof. Optional protective coatings for coating at least a portion of individual particles of such relatively lightweight and/or substantially neutrally buoyant materials include, but are not limited to at least one of phenol formaldehyde resin, melamine formaldehyde resin, urethane resin, or a mixture thereof. Other optional coating compositions known in the art to be useful as hardeners for such materials (e.g., coating materials that function or serve to increase the elastic modulus of the material) may be also employed in conjunction or as an alternative to protective coatings, and may be placed underneath or on top of one or more protective coatings. It will be understood by those of skill in the art that such protective and/or hardening coatings may be used in any combination suitable for imparting desired characteristics to a relatively lightweight and/or substantially neutrally buoyant particulate material, including in two or more multiple layers. In this regard successive layers of protective coatings, successive layers of hardening coatings, alternating layers of hardening and protective coatings, etc. are possible. Mixtures of protective and hardening coating materials may also be possible.
In another respect, disclosed is a relatively lightweight and/or substantially neutrally buoyant sand control material for use in a sand control method, such as gravel packing, that is a ground or crushed walnut shell material that is coated with a resin to substantially protect and water proof the shell. Such a material may have a specific gravity of from about 1.25 to about 1.35, and a bulk density of about 0.67. Size of such a material may be about 12/20 US mesh size. However other suitable sizes include sizes ranging from about 4 mesh to about 100 mesh. Advantageously, in some embodiments, such ground walnut shells may serve to attract fines and formation particles by their resinous nature, in some cases eliminating the need for smaller sizes. Applicability of larger sizes may depend on particular characteristics and requirements of a specific sand control application and method employed. In one embodiment for the manufacture of such particles for sand control applications (e.g., such as gravel packing or frac packing methods), an optional hardener may be applied to a ground walnut shell material first followed by a urethane coating as described elsewhere herein that may vary in amount as desired. For example, such a coating material may be present in an amount of from about 1% to about 20%, alternatively from about 10% to about 20% by weight of total weight of individual particles. Alternatively, such a coating material may be present in an amount of from about 2% to about 12% by weight of total weight of individual particles. Amount of resin may depend, for example, on price and application. In this regard, when employed for sand control methods such as gravel packing or frac packing, particulates may be first sprayed or otherwise coated with a hardener, and a coating may be applied to be about 12% by weight of total weight of the particle.
In one embodiment, the disclosed relatively lightweight particulate material may be introduced or pumped into a well as a neutrally buoyant particle in, for example, a saturated sodium chloride solution or any other completion or workover brine known in the art, for example, having a specific gravity of from about 1 to about 1.5, alternatively from about 1.2 to about 1.5, further alternatively about 1.2, thus eliminating the need for damaging polymer or fluid loss material. In one embodiment, such a material may be employed as sand control material at temperatures up to about 150xc2x0 F., and where subjected to formation closure stress, at closure stresses of up to about 1500 psi. However, these ranges of temperature and closure stress are exemplary only, it being understood that the disclosed materials may be employed as sand control materials at temperatures greater than about 150xc2x0 F. and, where present, at closure stresses greater than about 1500 psi, it also being understood with benefit of this disclosure that core and/or layer materials may be selected by those of skill in the art to meet and withstand anticipated downhole conditions of a given application.
Advantageously, in one frac pack embodiment the low specific gravity of the relatively lightweight particulate material may be taken advantage of to result in a larger width for the same loading (i.e., pound per square foot of proppant) to give much larger total volume and increased width for the same mass. Alternatively, this characteristic allows for smaller volumes of particulate material to be pumped while still achieving an equivalent width.
In yet another respect, disclosed is a method for treating a well penetrating a subterranean formation, including introducing a particulate material into the well; wherein at least a portion of individual particles of the particulate material each includes a core component of a first material at least partially surrounded by at least one layer component of second material, the first material of the particles including at least one of ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof, and the second material including a protective or hardening coating.
In another respect, disclosed is a sand control method for a wellbore penetrating a subterranean formation, including: introducing into the wellbore a slurry including particulate material and a carrier fluid; placing the particulate material adjacent the subterranean formation to form a fluid-permeable pack that is capable of reducing or substantially preventing the passage of formation particles from the subterranean formation into the wellbore while at the same time allowing passage of formation fluids from the subterranean formation into the wellbore; wherein at least a portion of individual particles of the particulate material each includes a core component of a first material surrounded by at least one layer component of second material, the first material of the particles including at least one of ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof, and the second material including a protective or hardening coating.
In yet another respect, disclosed is a sand control method for a wellbore penetrating a subterranean formation, including: introducing into the wellbore a slurry including particulate material and a carrier fluid; placing the particulate material adjacent the subterranean formation to form a fluid-permeable pack that is capable of reducing or substantially preventing the passage of formation particles from the subterranean formation into the wellbore while at the same time allowing passage of formation fluids from the subterranean formation into the wellbore. In this method, at least a portion of the individual particles of the particulate material may be substantially naturally buoyant in the carrier fluid and may include: a core component of a first material selected from at least one of ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof; and at least one layer component of second material surrounding the core component, the second material including a protective or hardening coating.